A typical liquid crystal display (LCD) device includes an LCD panel and a backlight module, and because the LCD panel is unable to emit light, a surface light source that evenly emits light should be provided by the backlight module. Generally, a lightbar is used as a light source of an edge-light backlight module. Because the lightbar emits additional heat, a lightbar heat sink is arranged to improve heat dissipation efficiency. Distance between a light emitting surface of the lightbar and a light incident surface of a light guide panel (LGP) is called light coupling distance and is a crucial optical parameter. When the light coupling distance is changed, optical performance of the backlight module is also changed. The light coupling distance should be strictly controlled to ensure optical quality of the backlight module. As shown in FIG. 1, in a typical method, a lightbar 1 is configured with a metal block 4, the metal block 4 is in contact with the light incident surface of the LGP 3, and a thickness of the metal block 4 is used to control the light coupling distance between the lightbar 1 and the LGP 3. However, because the metal block is fixed to the lightbar by a mount, disadvantages of the metal block include lower binding strength, unfirmness and easy disengagement when the backlight module is impacted by an outside force, thereby losing function of controlling the light coupling distance. In addition, because the lightbar is an electronic part, the lightbar is easy to deform when used as a structural part, thereby affecting the electrical properties.